Furnace for heat-treating objects under high pressure

ABSTRACT

A vertical furnace includes a press stand and a cylindrical pressure chamber suspended in the press stand. The pressure chamber includes a high-pressure cylinder and end members. The high-pressure cylinder includes a furnace chamber provided with insulation between the pressure cylinder and the walls of the pressure chamber. This insulation is a cylindrical sheath which depends from an end member fixed in one end of the high-pressure cylinder. The end closures include insulating bodies which extend into the furnace member.

United States Patent [72] inventor HansLundstrom Robertstors, Sweden [21 Appl. No. 866,887

[22] Filed Oct. 16, 1969 [45] Patented Dee. 21 1971 [73] Assignee Allnnnnn Svenske Elektrish Aktiebolaget Vasterls, Sweden [32] Priority Oct. 24, 1968 [33] Sweden [54] FURNACE FOR HEAT-TREATING OBJECTS UNDER HIGH PRESSURE 3 Claims, 2 Drawing Figs.

[$2] 0.8. CI 266/5 E [51] 1B1. C1 C2111 1/00 [50] Field 01 Search 75/226,

18/5 11, DIG. 26; 266/5 R, 5 E

[56] Relerenees Cited UNlTED STATES PATENTS 1,371,299 3/1921 Claude 18/D1G. 26

1,498,519 6/1924 Barton 266/5 R 1,500,789 7/1924 75/226 1,884,748 10/1932 266/5 R 2,341,860 2/1944 75/226 2,434,237 1/1948 75/226 3,198,503 8/1965 Eichelberg et al.. 266/5 R 3,419,935 1/1969 Pt'eiler et al 75/226X Primary Examiner-Gerald A. Dost AttorneyJennings Bailey, .Ir.

ABSTRACT: A vertical furnace includes a press stand and a cylindrical pressure chamber suspended in the press stand. The pressure chamber includes a high-pressure cylinder and end members. The high-pressure cylinder includes a furnace chamber provided with insulation between the pressure cylinder and the walls of the pressure chamber. This insulation is a cylindrical sheath which depends from an end member fixed in one end of the high-pressure cylinder. The end closures include insulating bodies which extend into the furnace member.

PATENTEUHEBEHM 3 628 779 SHEET 1 0F 2 Fig.

[WENT 1 US UK FURNACE FOR HEAT-TREATING OBJECTS UNDER HIGH PRESSURE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to cylindrical, preferably vertical furnaces for simultaneous treatment of a material at high temperatures, up to l,500 C. and high pressure, preferably 500 bar and above.

2. The Prior Art Furnaces of this kind are earlier disclosed in that U.S. Pat. applications, Ser. No. 676,623 filed on Oct. 9, 1967, entitled Vertical Tube furnace for isostatic Compression", now US. Pat. No. 3,470,303 and Ser. No. 855,911 filed on Sept. 8, 1969 and entitled Furnace for heat-treating objects under high pressure, both assigned to the assignee of the present application.

The furnaces make possible, for instance, pressure-sintering of powder bodies. By sintering under high pressure it is possible to achieve greater density than with sintering at atmospheric pressure and thus obtain better properties of the finished product in many respects. The sintering can also be carried out at lower temperatures than is possible at atmospheric pressure and the grain growth can therefore be limited during the sintering. The greater density and more favorable structure of the sintered product makes it stronger body arranged in the pressure chamber, the body consisting of an insulating sheath with insulating lid and bottom. The gas normally used, argon, which at the high operating pressure being used has very greatdensity but at the same time low viscosity, only 4-5 times that of air at atmospheric pressure, is thus very mobile. Since, in view of the density, it also has very great heat capacity, it is important that the heat-insulating hollow body is designed so that the least possible convection occurs between the actual furnace chamber and the inner walls of the pressure chamber so that the heat losses can be kept low. In conventional furnaces a cylindrical sheath has been used for insulation which rests on the lower end closure. The sheath is provided with a detachable lid which is removed before the finished product is withdrawn and replaced after the insertion of a new charge. Due to the pressure difference between the upper part of the furnace chamber and the gap between the insulating sheath and the high pressure cylinder, leakage between lid and insulating sheath causes hot gas to flow from the furnace chamber out into the gap. The heat loss causes increased power demands which may lead to uneven temperature distribution or may make it difficult or impossible to increase the temperature to the desired level. The time for an operating cycle is thus increased. If the worst comes to the words, the charge may even be damaged. The sealing between the lid and sheath of the insulation is thus essential for the function of the furnace, but it has proved difficult to make lid and sheath so that a completely reliable gastight seal is obtained.

SUMMARY OF THE DISCLOSURE The present invention relates to a furnace in which convection between the furnace chamber and the gap between the insulating sheath and high pressure cylinder is safely prevented. The invention is particularly suitable for furnaces where the axial pressure operating on the end closures in a pressure chamber is taken up by a separate, surrounding press stand. However, at low pressures threaded end closures may also be used.

The invention is essentially characterized in that the insulating cylindrical sheath is suspended on the upper end member. In the preferred embodiment this comprises a fixed ringshaped part on which the insulating cylindrical sheath is suspended and the opening of which forms the charging opening, and a lid projecting into the charging opening, in which lid of the insulation is suitably applied. The ring-shaped part end closure and the insulating sheath are connected to each other in a gastight manner by means of sealings ring.

BRIEF DESCRIPTION OF TI-IE DRAWINGS The invention will be further described with reference to the accompanying drawings.

FIG. 1 shows, partly in section, a furnace comprising a stationary high pressure chamber and a movable press stand to take up the axial forces operating on the end closures of the high pressure chamber.

FIG. 2 shows on a larger scale and in section, details of the end parts of the high pressure chamber.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the drawings 1 designates a press stand which is movable between the position shown in the drawing and a position where the stand surrounds the high pressure chamber 2. The press stand is of the type consisting of yokes 3 and 4, spacers 5 and a strip mantle 6. The stand is carried by wheels 7 running on rails 8. The high pressure chamber 2 is carried by a pillar 9 and contains a high pressure cylinder consisting of an inner tube 10, a surrounding prestressed strip sheath ill and end rings 12 which axially hold together the strip sheath and form the suspension means by which the high pressure chamber is attached to the pillar 9. The chamber 2 has a lower end closure 13 which projects into the tube 10 of the high pressure cylinder. In the end closure is a groove into which is inserted a sealing ring 14, a channel 15 for the supply of pressure medium and a channel 16 for cables to feed heating elements 17 to heat the furnace. The elements 17 are supported by a cylinder 18 which rests on an insulating bottom 19 which projects into an insulating sheath 20. The upper end closure has an annular part 21 with a sealing ring 22 which seals against the tube 10. The sheath 20 is suspended in the part 21 and connected in a gastight manner to this. The end closure also has a lid 23 to close the opening in part 21 which is usually fixed in the high pressure cylinder. The lid is provided with a sealing ring 24 which seals against the inner surface of the part 21 and with an insulating lid 25 which, when the high pressure chamber is sealed, projects into the cylinder 20 and forms part of the insulating shell surrounding the actual furnace chamber 26. The lid 23 is attached to a bracket 27 supported by an operating rod 28 which can be raised, lowered and turned.

FIG. 2 shows on a larger scale part of the high pressure chamber 2 with the end closures projecting into the tube 10 of the high pressure cylinder. The insulating sheath 20 is conventionally constructed of a number of metal tubes 29, 30 and 31 with intermediate layers 32 and 33 of insulating material and a connecting ring 34. In furnaces of known design the insulating lid 25 has been scaled to the ring 34 after each charge has been inserted. This is time consuming and since the seal could not be effectively cooled it required great care in applying the seal. If, due to temperature fluctuations, cracks were formed between the lid and the ring 34, hot pressure medium flowed out radially past the insulatingv sheath between the ring 34 and the end closure and was cooled upon contact with the wall of the tube 10. By connecting the ring 34 to the annular part 21 so as it is permit the sheath 20 to hang in the upper end closure, the horizontal flow of hot pressure medium from the upper part of the furnace chamber 36 to the gap 35 between the tube 10 and sheath 20 is effectively prevented. Thus an effective seal between the lid 25 and the sheath 20 is unnecessary. Between the ring 34 and the part 21 a seal 36 is inserted which is permanent and can be effectively cooled. The lid 25 includes a sheet metal dome 37 filled with insulating material and connected to the lid 23 by a flange 38.

The invention is of course not limited to the embodiments shown in the drawings. Many variations are feasible within the scope of the following claims.

lclairn:

1. Vertical furnace for simultaneously treating material at high temperatures and in a gas atmosphere of high pressure, comprising a press stand, a cylindrical pressure chamber suspended in said press stand and comprising a high pressure cylinder and end members for closing gastightly the pressure cylinder which are held in place by said press stand and take up the axial forces which a pressure medium in the pressure chamber exerts on the end members, a furnace chamber within the high pressure cylinder, means to supply high pressure fluid to the furnace chamber, insulation arranged between said furnace chamber and the walls of the pressure chamber, which insulation comprises a cylindrical sheath of insulating material and an insulating lid and bottom, in which the insulating cylindrical sheath is suspended from the upper end member.

2. Furnace according to claim 1, in which the upper end member comprises a fixedly attached ring-shaped part from which the insulating cylindrical sheath is suspended and the opening of which forms the charging opening and a removable lid having a part projecting into the charging opening.

3. Furnace according to claim 1, in which the cylindrical sheath is spaced inwardly from the inner wall of the pressure chamber and terminates short of the bottom of the pressure chamber.

i 8 i i 

1. Vertical furnace for simultaneously treating material at high temperatures and in a gas atmosphere of high pressure, comprising a press stand, a cylindrical pressure chamber suspended in said press stand and comprising a high pressure cylinder and end members for closing gastightly the pressure cylinder which are held in place by said press stand and take up the axial forces which a pressure medium in the pressure chamber exerts on the end members, a furnace chamber within the high pressure cylinder, means to supply high pressure fluid to the furnace chamber, insulation arranged between said furnace chamber and the walls of the pressure chamber, which insulation comprises a cylindrical sheath of insulating material and an insulating lid and bottom, in which the insulating cylindrical sheath is suspended from the upper end member.
 2. Furnace according to claim 1, in which the upper end member comprises a fixedly attached ring-shaped part from which the insulating cylindrical sheath is suspended and the opening of which forms the charging opening and a removable lid having a part projecting into the charging opening.
 3. Furnace according to claim 1, in which the cylindrical sheath is spaced inwardly from the inner wall of the pressure chamber and terminates short of the bottom of the pressure chamber. 